Which nation established dominion over South Africa in 1902?

Great Britain established control over South Africa in 1902 after defeating the Boer republics in the Second Boer War.

The war, also called the South African War or Anglo-Boer War, lasted from 1899 until 1902. Britain fought the South African Republic, commonly called the Transvaal, and the Orange Free State. The conflict ended with the Treaty of Vereeniging, signed on 31 May 1902, which brought the two Boer republics under British rule.

The wording can cause a common historical mix-up. South Africa did not become a unified British dominion in 1902. The Transvaal and Orange River Colony were first administered as separate British colonies. The Union of South Africa was created later, on 31 May 1910, by joining four colonies: the Cape, Natal, Transvaal and Orange River colonies.

Thus Great Britain is the correct nation for the 1902 change in sovereignty, while 1910 is the key date for the formal Union of South Africa as a self-governing dominion within the British Empire.